Among raw materials for the preparation of polymer products, the processing of acrylic monomers has undergone rapid development in recent years. Acrylic monomers are used predominantly in the production of fibers, dispersions, raw materials for coatings, raw materials for adhesives, and thermoplastic compositions. In smaller amounts, they serve as starting materials for a variety of chemical syntheses.
In this context, polymers based on acryloyl- and/or methacryloylpolyoxyalkylenes are also of increasing interest. By controlling the variation of the polyoxyalkylene units, it is possible to obtain monomers having a custom-tailored solubility behavior, which can then be reacted alone or in combination with other olefinically unsaturated compounds to form polymers. Compounds of this kind are used, for example, as auxiliaries in the formulation of aqueous inks, as described in DE-A-196 54 752. A further field of use of such compounds is in the dispersion of pigments for preparing water-thinnable coating materials, as is described in EP-A-0 803 556 and JP-A-092 670 34. It is therefore not surprising that acryloyl- and/or methacryloylpolyoxyalkylenes are also obtainable commercially (from Nippon Oil and Fats Co.).
For the purposes of this invention, "acryloyl" or "methacryloyl" means a radical of the general formula: ##STR2##
where R is CH.sub.3 or H.
Processes for the preparation of acryloyl- and/or methacryloylpolyoxyalkylenes have already been described.
In addition to processes for the esterification and transesterification of acrylates and/or methacrylates, which correspond essentially to literature preparation processes for carboxylic esters, as described, for example, in J. March, Advanced Organic Chemistry, Wiley, 1992, there are also specifically adapted processes which are known in connection with the modification of polyoxyalkylenes.
In this context, it is common to start from hydroxy-functional precursors and to introduce the acryloyl and/or methacryloyl group by esterification or transesterification processes; starting from the corresponding acrylic and/or methacrylic esters or acrylic and/or methacrylic acids. Generally, metal salts or their organic complexes or acids are used in this case. For instance, DE-A-19 535 936 describes the acrylation of polyether polyols with catalysis by p-toluenesulfonic acid and hypophosphorous acid using an azeotrope former and additional free-radical scavengers at temperatures of 80-100.degree. C. This and similar processes are generally carried out at temperatures above 80.degree. C., in particular above 100.degree. C., and require additional stabilization of the reaction mixture by free-radical scavengers (for example methylhydroquinone), in order to reliably suppress unwanted polymerization of the acryloyl and/or methacryloyl compounds at these temperatures.
For many fields of application, the catalyst must subsequently be removed, or at least neutralized, in order to avoid unwanted side reactions. This requires a complex workup procedure, in which metal oxides, metal hydroxides or corresponding salts of the metals and/or of the acids used as catalyst are formed and then, in general, removed by filtration. Such filtrations of acryloyl- and/or methacryloyl-containing reaction mixtures are complex from a technological and industrial safety standpoint and, consequently, are often lengthy.
Because of the high temperature, acryloyl- and/or methacryloyl-functional compounds prepared in this way frequently have an intense coloration (yellow to brownish black). This frequently prohibits the direct use of such acryloyl and/or methacryloyl compounds in applications wherein coloration requirements of the raw materials are stringent (for example, their use as reactive diluents in radiation-curing clearcoats or their use as a raw material for polyacrylates for the cosmetics industry).
In order to avoid some of the disadvantages described above, U.S. Pat. No. 4,528,334 describes a one-pot reaction to carry out the polymerization of acrylic acid in the presence of polyoxyalkylenes; the formation of corresponding polyoxyalkylene-modified polyacrylic acid being achieved at temperatures above 145.degree. C. In the case of this process, the required high temperatures are disadvantageous. Furthermore, the use of other monomers from the important and wide-ranging family of the acrylic and/or methacrylic esters would result in an uncontrollable sequence of transesterification reactions which therefore restrict the process greatly in terms of its variability.
In order to obtain satisfactory yields under mild reaction conditions, it is common to use particularly reactive acrylic and/or methacrylic acid derivatives. Reactions of polyoxyalkylene compounds with acryloyl and/or methacryloyl halides, generally the chlorides, are described, inter alia, in Polym. J., Vol. 17, 827 ff., Polym. Bull., Vol. 15, 425 ff. and Colloid Polym. Sci., Vol. 275, 227-233.
The reaction of acrylic and/or methacrylic anhydrides with polyoxyalkylene compounds is described in Macromolecules, Vol. 30, 6489-6493.
These processes are limited in their spectrum of use as a result of the handleability of the reactive acryloyl and/or methacryloyl halides and acrylic and/or methacrylic anhydrides. Specifically, the requirements with respect to storage conditions; the need to exclude even the slightest trace of moisture; and also the general industrial safety conditions are so high that commercial use of such processes is opposed by an often unjustifiable expense.
R. Tor, Enzyme Micro. Technol., 1990, Vol. 12, April, pp. 299-304, describes the enzymatically catalyzed transesterification of acrylic and methacrylic monomer esters for the preparation of hydroxy- and dihydroxyalkyl acrylates and methacrylates without the formation of di- or triacrylates and -methacrylates. 2-hydroxyethyl, 2-hydroxypropyl and 1,2-dihydroxypropyl esters of acrylic acid and methacrylic acid are investigated in the R. Tor disclosure.